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Share-Based Payment Arrangements (Detail) - Assumptions used to determine fair value of options granted (USD $)
12 Months Ended
Dec. 31, 2012
Sep. 30, 2010
Minimum [Member]
Sep. 30, 2010
Maximum [Member]
Sep. 30, 2010
Weighted Average [Member]
Weighted average fair value of awards issued (in Dollars)       $ 6.67
Assumptions        
Expected volatility 35.40% 65.00% 66.20%  
Weighted-average volatility       65.40%
Expected dividends       1.77%
Expected term (years)       4 years 9 months
Risk-free rate 2.50% 2.20% 2.70%